Manchester United centre-back Chris Smalling said post-match that manager Jose Mourinho posed a simple question to his players at half-time: "Do you want to be the clowns who stand there watching Manchester City get the trophy?" It turned out to be precisely the motivation the Red Devils needed to finally stand up and be counted in what eventually was a thrilling Manchester derby that saw United stage a spectacular comeback, cancel out a two-goal deficit and win 3-2.

The win delayed City's trophy celebrations as they need another win to cement the Premier League title. Pep Guardiola's men are still the favourites to be the league champions, and getting that a win with six games to go is just a formality. However, the Spaniard would be anxious about his team's inability to put the game to bed after having taken a 2-0 lead on Saturday. City wasted a glut of chances, Raheem Sterling being the chief culprit, and what could have been a five-goal lead at half-time ended up being just two. It might sound pompous but a two-goal lead was the bare minimum given how good Guardiola's side were and the chances they created.

Manchester United's Paul Pogba scores their first goal against Manchester City in the Premier League. Reuters

More than the loss itself, it would be the manner of it that would concern the former Barcelona and Bayern Munich coach. This was the second match in a row that his team had conceded three goals in the space of 15-20 minutes. Their capitulation in defence was pretty embarrassing and gave another insight into the team's weakness that opponents could potentially exploit.

Indeed, City is generally great on the ball, calm in possession and scintillating in attack. These are some of their qualities that shine and inspire other teams. However, their defensive fallibility remains and is their Achilles heel, as demonstrated by both Liverpool in the Champions League and United on Saturday. The fact that the Sky Blues had managed to put in a brilliant first-half performance despite resting regulars like Kevin De Bruyne and Kyle Walker, and went in to the match resting both their strikers, spoke volumes of the depth in their squad.

Despite the positives, it would be the mental impact of the derby loss that Guardiola would be worried about, especially considering that they need to produce an incredible comeback of their own to overcome a three-goal deficit and get past Liverpool in the quarter-finals of Europe's top club competition.

For Mourinho, it was a win that showed him what his team could do, especially when they play with a slightly higher tempo, with an attacking mindset. Too often in big matches, the Portuguese tactician have been relying on a direct approach to score goals and focusing on ensuring defensive solidity and caution. That did not work for them in the first half against City, a team that thrive on being given more of the ball. What did work very well for the Red Devils, however, was the change in mindset in the second half. United were sharper, pressed their opponents higher up the field and played with an intent to attack and get back into the game.

A lot of that positive change was brought about by the two most-expensive attacking talents in the team, Paul Pogba and Alexis Sanchez. The former was a picture of poise and power, using his natural athleticism and ability to run to get into great attacking positions, getting into tackles to disrupt play and trying his best to make a nuisance of himself for the opposition. Sanchez, on the other hand, dropped deep to pick the ball up on many occasions, ran at the opposition defence and worked himself into the ground trying to create openings for his team.

It wasn't a surprise to see that Pogba scored two of the three goals, while the Chilean was the only player to have had a hand in all three goals, assisting two of them. It was the first time that the two of them showed that they could dovetail beautifully, alternating in their roles and responsibilities to accommodate each other.

As is the case, not many Manchester United matches go without a mention of David de Gea and his brilliance. One of the players at fault for City's second goal which came from his bad clearance, the Spain goalkeeper redeemed himself with a remarkable one-handed save from Sergio Aguero. When City did get past him in the second half, they were thwarted by the post.

The match was also important for Mourinho. The Manchester United manager has been criticised for his tactics and for refusing to let go of his defence-first mentality even at a club like United, where attacking traditions have been the norm. By spearheading this comeback against City, he showed he still has the dressing room, that his teams can attack when they are allowed to and that he ought to play with the handbrake off on more occasions.

It also showed exactly why he had asked the club to pay £89 million to sign Pogba and proved that the midfielder can perform the tasks required of him on a consistent basis, given that there is stability offered like the one provided by the midfield duo of Nemanja Matic and Ander Herrera on Saturday. The Serbian was his usual solid self while Herrera had a good day as well, passing the ball well and with confidence and providing a refresher in game management, resorting to the dark arts when needed to thwart the danger.

Most of all, it showed Manchester United that they have what it takes to challenge the biggest teams, but what separates them from the very top teams at the moment is the consistency needed to win. Last night's win was a big mental victory and hopefully, they would thrive going forward. For Manchester City, it was a minor blip on the road to the league title, but a bigger reminder of the flaws that are slowly coming to the fore in their team, and that is something for Guardiola to address going forward.

Yes, Manchester has been blue this season, but last night, the city was definitely red as the traditional heavyweights gave the upstarts a reality check and dented their aura of invincibility. Finally, the rivalry everyone expected when Guardiola and Mourinho arrived in the city, has started to develop. Hopefully, next season would be when these two coaches would take it to the next level.